The present invention relates to a vibration drill unit equipped with features of giving rotations and vibrations to a drill.
A conventional vibration drill unit is normally used for drilling a material to be drilled, such as, concrete, mortar, and tiles. The basic structure of a conventional vibration drill unit is described as follows.
the conventional vibration drill unit is provided with a spindle, which is driven and rotated by a motor, movably in an axial direction, and a second ratchet, which is not rotatable but movable in the axial direction, and is disposed on a first ratchet coupled to the spindle so as to be opposed to the first ratchet. The second ratchet is pressed by a spring in the axial direction to cause claws formed on the second ratchet to be engaged with claws formed on the first ratchet.
In such a conventional vibration drill unit, it is possible to select, as an operation mode, a drill mode in which only rotations are given to a drill, or a vibration drill mode in which rotations and vibrations are given to the drill at the same time. When the vibration drill mode is selected, the spindle is also movable in the axial direction. If the drill is pushed to a material to be drilled, the second ratchet moves in the axial direction to the spindle along with the main body frame, and the second ratchet is brought into contact with the first ratchet, wherein the claws of both are engaged with each other.
Therefore, by the first ratchet rotating along with the spindle in the vibration drill mode, the claw of the second ratchet gets over the claw of the first ratchet, and the second ratchet repeats being brought into contact with and separating from the first ratchet, thereby causing the spindle to vibrate in the axial direction. Since the vibration is transmitted from the spindle to a drill via the drill chuck, the drill is given vibrations and rotations at the same time. Thus, a drilling work of a material to be drilled can be efficiently carried out by the drill.
Herein, FIGS. 7(a) through 7(c) show the shapes of respective claws 34a and 35a of the first ratchet 34 and the second ratchet 35 of a conventional vibration drill unit, and states where the claws are engaged with and are disengaged from each other. Conventionally, the respective claws 34a and 35a forming ridges of the first ratchet 34 and the second ratchet 35 are composed of inclined surfaces 34a-1 and 35a-1 having a gentle inclination and inclined surfaces 34a-2 and 35a-2 having a steep inclination.
In this connection, as shown in FIG. 7(a), since the inclined surfaces 34a-1 and 35a-1 of the respective claws 34a and 35a of the first ratchet 34 and the second ratchet 35 are engaged with each other when the first ratchet 34 rotates in the direction of the arrow, both the ratchets 34 and 35 are spaced from each other in the axial direction, in the up and down direction of drawings as shown in FIG. 7(b). After that, since the second ratchet 35 is brought into contact with the first ratchet 34 by a pressing force of a spring (not illustrated), the inclined surface 35a-1 of the claw 35a of the second ratchet 35 is brought into contact with the inclined surface 34a-1 of the claw 34a of the first ratchet 34 as shown in FIG. 7(c). At this time, the second ratchet 35 gives an impact force F (illustrated) to the first ratchet 34.
Conventional vibration drill units as described above are disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2005-052905 and Japanese Registered Utility Model Publication No. 3041486
As shown in FIGS. 7(a)-(c), in the conventional vibration drill unit, the first ratchet 34 and the second ratchet 35 are brought into collision with each other at the inclined surfaces 34a-1 and 35a-1 of the respective claws. At the time of such collision, the impact force F given from the second ratchet 35 to the first ratchet 34 in part operates on the inclined surface 35a-1 in the axial direction. However, the force F is truly applied to the first ratchet 34 in a direction which is inclined by an angle θ to the axial direction. Therefore, the component of the force F in the axial direction Fx=F cos θ is smaller than the impact force F (Fx<F). Thus, it cannot be said that the entire kinetic energy which the second ratchet 35 imparts to the first ratchet 34 is utilized for vibrations in the axial direction. Therefore, there is a problem in that the energy loss in conventional vibration drill units is great.
Also, as illustrated in FIG. 7(c), Fy=F sin θ shows the component of the impact force F in the direction orthogonal to the axial direction. In addition, in FIG. 7(a), reference numerals 34a-3 and 35a-3 denote the top parts of the respective claws 34a and 35a, respectively.
Also, since the respective claws 34a and 35a of the first ratchet 34 and the second ratchet 35 are not brought into collision with each other at the bottom (valley) parts thereof, but are brought into collision with each other at the inclined surfaces 34a-1 and 35a-2, the stroke S of the second ratchet 35 in the axial direction is small, and the relative speed of the second ratchet 35 is small when it was brought into collision with the first ratchet 34.
Due to the above reasons, the drilling performance of conventional vibration drill units is insufficient.